Three weeks after Mr. Obama told an audience at Kennedy Space Center that he wants to land astronauts on an asteroid by 2025, Congress remains unconvinced, largely because Mr. Obama's proposal also puts commercial rocket companies in charge of getting astronauts to the International Space Station after the space shuttle is retired this year.

Few Democrats have publicly endorsed the entire plan, while opponents such as Alabama Republican Sen. Richard Shelby, who looks after the interests of NASA's Marshall Space Flight Center in Huntsville, continue to blast the proposal as "unrealistic" and "destructive."

NASA itself also appears to be hedging its bets that the president's vision might not pass muster with Congress. KSC officials and contractors, under direction from Johnson Space Center and NASA Administrator Charlie Bolden, are pressing ahead with plans for test flights of a multibillion-dollar Ares I rocket that Mr. Obama wants to cancel.

Meanwhile, aerospace contractors are trying to sell members of Congress on an $8 billion rocket that could be fashioned from pieces of the shuttle, which is supposed to be retired later this year. Last week, a group of contractors led by aerospace giant Boeing Co. met Sen. Bill Nelson, D-Fla., to push the new rocket idea. Mr. Nelson previously has backed more Ares test flights.

There is little unity in Congress on what to do, but most experts agree it could stall or even derail White House aims to retire the shuttle and to cancel NASA's long-standing plans to return astronauts to the moon.

Key is what to do with Constellation, a spacecraft program that has consumed more than $9 billion in federal funds in five years.

When first conceived, NASA had planned on using its Ares rockets and Orion capsule to return astronauts to the moon by 2020. But financial and technical woes have made that goal impossible, and Mr. Obama wants to cancel everything in Constellation but the crewed Orion capsule so that NASA could focus on new technology that could enable a future asteroid mission.

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